There are many refractive errors associated with the human eye. When the focal point of images is formed in front of the retina/macula region due to excess refraction of light rays, the refractive error is called myopia or near-sightedness. When, on the other hand, the focal point of images lie outside the eye behind the retina/macula region due to insufficient refraction of light rays, the refractive error is called either hyperopia or far-sightedness or presbyopia. These problems can be surgically corrected by either changing the eye length or corneal curvatures. In case of presbyopia, as individuals age, the human eye loses its ability to focus on nearby objects. This condition, known as presbyopia, is due to a progressive loss in the elasticity of the lens of the eye, such that the ciliary muscles which normally force the lens, through the action of zonule fibers on the lens capsule, in a rounded shape to accommodate near objects can no longer exert the necessary changes in the lens' shape.
The conventional ophthalmic and/or optometric solution to the problems of myopia, hyperopia, and presbyopia is a prescription of glasses, contact lenses or reading glasses or, for individuals who already require glasses to correct other refractive errors such as myopia or astigmatism, a prescription of bifocal or multifocal glasses.
This century has witnessed a revolution in the surgical treatment of ophthalmic disorders and refractive errors of the human eye. This revolution ranges from corneal implantations, cataract extraction, phacoemulsification of the lens, intraocular lens implantation, glaucoma implants to control the intraocular pressure, radial keratotomy, excimer laser ablation of the cornea, trabeculoplasty, iridotomy, virectomy, and the surgical buckle treatment of retinal detachment. The recent surgical solutions to myopia, hyperopia, and astigmatism have been laser photorefractive keratectomy (PRK). Lasik (laser-assisted in-situ keratomileusis) and RK or radial keratotomy. Modern techniques proposed to correct human eye refractive errors have been corneal implants (Intacs, Silvestrini, et al.) intrastromal corneal ring (ICR, Silvestrini, et al.) and scleral implants (SASI, Schachar, et al.), smart bands (Shahinpoor, et al.) as well as conductive keratoplasty (CK, Mendez, et al.).
The effective focal length of the human eye must be adjusted to keep the image of the object focused as sharply as possible on the retina. This change in effective focal length is known as accommodation and is accomplished in the eye by varying the shape of the crystalline lens. This is necessary for the human eye to have clear vision of objects at different distances. Generally speaking, in the unaccommodated normal vision, the curvature of the lens is such that distant objects are sharply imaged on the retina. In the unaccommodated eye, close objects are not sharply focused on the retina an their images lie behind the retinal surface. In order to visualize a near object clearly, the curvature of the crystalline lens is increased, thereby increasing its refractive power and causing the image of the near object to fall on the retina. The change in shape of the crystalline lens is accomplished by the action of ciliary muscle by which the radial tension in the lens is reduced, according to classical Helmholtz theory of accommodation, and it becomes more convex.
Based on Helmholtz theory, in the unaccommodated human eye the lens and its capsule are suspended on the optical axis behind the pupil by a circular assembly of many radially directed collagenous fibers, the zonules, which are attached at their inner ends to the lens capsule and at their outer ends to the ciliary body, a muscular constricting ring of tissue located just within the outer supporting structure of the eye, the sclera. The ciliary muscle is relaxed in the unaccommodated eye and therefore assumes its largest average diameter. Here by average diameter is meant the half of the maximum plus the minimum diameters possible. According to the Helmholtz classical theory of accommodation, the relatively large average diameter of the ciliary body in this unaccommodated condition, causes a tension on the zonules which in turn pull radially outward on the lens capsule, making it less convex. In this state, the refractive power of the lens is relatively low and the eye is focused for clear vision of distant objects. When the eye is intended to be focused on a near object, the muscles of the ciliary body contract. This contraction causes the ciliary body to move forward and inward, thereby relaxing the outward pull of the zonules on the equator of the lens capsule and reducing the zonular tension on the lens. This allows the elastic capsule of the lens to contract causing an increasing in the sphericity of the lens, resulting in an increase in the optical refraction power of the lens. Recently, Schachar (whose inventions are discussed below) has proposed a radically different theory of accommodation which refutes the Helmholtz theory.
U.S. Pat. No. 5,354,331 to Schachar discloses how presbyopia and hyperopia are treated by a method that increases the amplitude of accommodation by increasing the effective working distance of the ciliary muscle in the presbyopic eye. This is accomplished by expanding the sclera in the region of the ciliary body. A relatively rigid band having a average diameter slightly greater than that of the sclera in that region is sutured to the sclera in the region of the ciliary body. The scleral expansion band comprises anterior and posterior rims and a web extending between the rims, the anterior rim having a smaller average diameter that the posterior rim.
U.S. Pat. No. 5,465,737 to Schachar the teachings are similar to those of the '331 patent, except that by weakening the sclera overlying the ciliary body, by surgical procedures or treatment with enzymes, heat or radiation, whereby intraocular pressure expands the weakened sclera, or by surgical alloplasty. The effective working distance of the ciliary muscle can also be increased by shortening the zonules by application of heat or radiation, by repositioning one or both insertions of the ciliary muscle or by shortening the ciliary muscle. Presbyopia is also arrested according to the invention by inhibiting the continued growth of the crystalline lens by application of heat, radiation or antimitotic drugs to the epithelium of the lens. Primary open angle glaucoma and/or ocular hypertension can be prevented and/or treated by increasing the effective working range of the ciliary muscle according to the invention.
U.S. Pat. Nos. 5,489,299; 5,722,925; 5,503,165; and 5,529,076 to Schachar contain essentially the same ideas as U.S. Pat. Nos. 5,354,331 and 5,465,737 with some improvements such that presbyopia and hyperopia are treated by a method that increases the amplitude of accommodation by increasing the effective working distance of the ciliary muscle in the presbyopic eye. The effective working distance of the ciliary muscle is increased by shortening the zonules by application of heat or radiation, by repositioning one or both insertions of the ciliary muscle or by shortening the ciliary muscle. Presbyopia is also arrested by inhibiting the continued growth of the crystalline lens by application of heat, radiation or antimitotic drugs to the epithelium of the lens. Primary open angle glaucoma and/or ocular hypertension can be prevented and/or treated by increasing the effective working range of the ciliary muscle.
U.S. Pat. No. 6,007,578 to Schachar discloses how presbyopia is treated by implanting within a plurality of elongated pockets formed in the tissue of the sclera of the eye, transverse to a meridian of the eye, a prosthesis having an elongated base member having an inward surface adapted to be placed against the inward wall of the pocket and having a ridge on the inward surface of the base extending along at least a major portion of the major dimension of the base. The combined effect of the implanted prostheses is to exert a radially outward traction on the sclera in the region overlying the ciliary body which expands the sclera in the affected region together with the underlying ciliary body. This restores the effective working distance of the ciliary muscle in the presbyopic eye and thereby increases the amplitude of accommodation. Hyperopia, primary open angle glaucoma and/or ocular hypertension can be treated by increasing the effective working distance of the ciliary muscle.
U.S. Pat. No. 6,006,756 to Shadduck, discloses a system and technique called magnetoresonant induction of an intrastromal implant that is adapted for corneal re-shaping. The technique is utilized to correct mild to high hyperopia and presbyopia by steepening the anterior corneal curvature in a single treatment, or in periodic treatments over the lifetime of the patient. The system comprises a combination of components including (i) at least one implantable magnetoresonant intrastromal segment, and (ii) an oscillating magnetic field generator together with a dosimetry control system including at least one emitter body adapted for positioning proximate to the patient's eye and intrastromal implant. The system can deliver thermal effects to appropriate stromal lamellae by non-contact inductive heating of the implant which in turn contracts or compresses stromal collagen fibrils into a circumferential cinch about an anterior layer of the cornea and steepens the anterior corneal curvature. A dosimetry control system controls the power level and duration of exposure of the oscillating magnetic field(s) and may be combined with intraoperative corneal topography.
U.S. Pat. No. 5,147,284 to Fedorov, et al., teaches a device for restoration of visual functions in cases of affected optic nerve and retina with an electromagnetic field radiator emitting the latter field into the region of the eyeball and an electromagnetic field receiver adapted to interact with the radiator. Both of these exert an electrostimulation effect on the optic nerve and the retina. The electromagnetic field radiator is a source of a pulsed magnetic field and is shaped as an electromagnet provided with an adjuster of a distance between the end of the electromagnet and the electromagnetic field receiver, which is in effect an inductor having lead wires furnished with electrodes whose active surface exceeds 10 mm2. A method for restoration of visual functions in cases of affected optic nerve and retina consists in conducting electrostimulation of the eyeball, for which purpose an inductor is implanted into the orbit on the sclera of the posterior portion of the eyeball in such a manner that one of the inductor electrodes is positioned nearby the external tunic of the optic nerve, while the other electrode is fixed on the sclera in the area of the eyeball equator, whereupon a pulsed magnetic flux is applied remotely to the eyeball portion carrying the inductor, the magnetic field induction being from 0.1 T to 0.25 T, while the pulsed magnetic field is simultaneously brought in synchronism with pulsation of the internal carotid artery.
U.S. Pat. No. 5,782,894 to Israel discloses a device and method for treating presbyopia by which the ciliary muscles of the eyes are electrically stimulated when the internal rectus muscles of the eyes are activated in order to focus the eyes on objects within the near field of vision. The amounts of electrical stimulation can be adjusted according to the individual needs of a patient and are preferably in direct proportion to the amounts of contraction of the internal muscles.
U.S. Pat. No. 4,961,744 to Kilmer, et al, discloses a surgical apparatus for inserting a plastic, split end, adjusting ring into the stroma of the cornea of the eye wherein the adjusting ring includes, as a part thereof, a dissecting head to part the stroma and provide a pathway for the adjusting ring as the ring is rotated. The ends of the adjusting ring are moved to change the shape of the cornea to a desired shape in accordance with the desired visual correction after which the ends of the adjusting ring are fixably joined to maintain the desired shape.
U.S. Pat. No. 5,300,118 to Silvestrini, et al., discloses an intrastromal corneal ring (ICR) that is adjustable in thickness and has an elongated, flexible, preferably transparent or translucent body which forms a circle. The ICR is of a size such that it can be inserted into a human eye and is comprised of a material which is compatible with human ocular tissue. The thickness of the ring can be adjusted so that it is not necessary to stock a plurality of different rings of different sizes to be used in connection with a method of adjusting the shape of the cornea of the eye. A plurality of different embodiments of ICRs are disclosed each of which are adjustable in terms of their thickness. The thickness may be adjusted prior to the insertion of the ICR into the cornea and may not be further adjustable after insertion. However, in accordance with preferred embodiments, the ICR is inserted at a thickness which is believed to be proper and may thereafter be further adjusted in order to precisely define the desired thickness and thereby more precisely adjust the shape of the cornea, and focus the light entering the eye on the retina.
U.S. Pat. No. 5,824,086 to Silvestrini discloses a pre-formed intrastromal corneal insert. It is made of a physiologically compatible polymer and may be used to adjust corneal curvature and thereby correct vision abnormalities. The insert or segment may also be used to deliver therapeutic or diagnostic agents to the interior of the cornea or of the eye. The insert subtends only a portion of a ring or “arc” encircling the anterior cornea outside of the cornea's field of view. The invention also includes a procedure for inserting the device into the cornea.
U.S. Pat. No. 6,051,023 to Kilmer, et al., discloses a surgical apparatus for inserting a plastic, split end, adjusting ring into the stroma of the cornea of the eye wherein the adjusting ring includes, as a part thereof, a dissecting head to part the stroma and provide a pathway for the adjusting ring as the ring is rotated. The ends of the adjusting ring are moved to change the shape of the cornea to a desired shape in accordance with the desired visual correction after which the ends of the adjusting ring are fixably joined to maintain the desired shape.
U.S. Pat. No. 5,888,243 to Silverstrini discloses an intrastromal corneal ring housing comprising at least one outer layer of a physiologically compatible polymer having a low modulus of elasticity, which polymer may be hydratable and may be hydrophilic. The inner portion of the hybrid intrastromal corneal ring may be hollow or may contain one or more physiologically compatible polymers.
U.S. Pat. No. 5,766,171 to Silvestrini teaches a device and procedure for the correction of optical abnormalities in a human eye. It involves use of an inventive electrosurgical energy probe with specific physical configurations. The process preferably utilizes a high frequency RF electro-desiccation or ablation device. The procedure involves the initial step of forming at least one access site allowing access to the corneal volume behind the Bowman's Layer. It is placed in the anterior surface of the cornea through and ending posterior to the Bowman's layer of the eye. The electrosurgical probe is then introduced into the access site, and depending upon the visual abnormality to be corrected, the probe is activated to adjust the volume of the corneal stromal layers through ablation or desiccation. The shape of the volume desiccated or ablated is dependent upon the aberration to be corrected. In other instances, such as for the treatment of astigmatism, certain smaller sections of the corneal volume may be shrunk. In certain circumstances, the Bowman's layer may be cut to allow the curvature of the cornea to change after the corneal volume adjustment. These relief cuts may be radial, circular, semicircular or any other form appropriate for the option adjustment needed.
U.S. Pat. No. 6,214,044 to Silvestrini teaches an intrastromal corneal ring having comprising at least one outer layer of a physiologically compatible polymer having a low modulus of elasticity, which polymer may be hydratable and may be hydrophilic. The inner portion of the hybrid intrastromal corneal ring may be hollow or may contain one or more physiologically compatible polymers.
U.S. Pat. No. 6,966,927 to Silvestrini presents a hybrid intrastromal corneal ring (“ICR”) comprising at least one outer layer of a physiologically compatible polymer having a low modulus of elasticity, which polymer may be hydratable and may be hydrophilic. The inner portion of the ICR may be hollow or may contain one or more physiologically compatible polymers.
U.S. Pat. No. 6,213,997 to Hood and Mendez teaches a thermokeratoplasty system and method for locally heating and reshaping a cornea in a manner that produces a minimal regression of the corneal correction. The system includes a probe that is coupled to a power source which can provide current at a predetermined power, frequency and time duration. The probe has a sharp tip that is inserted into the stroma of the cornea. The tip has an insulated stop that controls the depth of tip penetration. Current flows into the cornea through the probe tip to locally heat and denature the corneal tissue. The denatured tissue causes a subsequent shrinkage of the cornea. A pattern of denatured areas can be created around the cornea to correct the vision of the eye.
U.S. Pat. No. 7,018,377 to Hood and Mendez also teaches a thermokeratoplasty system and method for locally heating and reshaping a cornea in a manner that produces a minimal regression of the corneal correction. The system includes a probe that is coupled to a power source which can provide current at a predetermined power, frequency and time duration. The probe has a sharp tip that is inserted into the stroma of the cornea. The tip has an insulated stop that controls the depth of tip penetration. Current flows into the cornea through the probe tip to locally heat and denature the corneal tissue. The denatured tissue causes a subsequent shrinkage of the cornea. A pattern of denatured areas can be created around the cornea to correct the vision of the eye.
U.S. Pat. No. 6,849,090 to Nigam also describes a bio-compatible corneal ring for myopic correction and accommodation for presbyopia. The corneal ring is made from a bio-compatible material with a lens body having an inner and outer circular edge. The inner circular edge forms an opening in the lens body. The posterior surface of the lens body has a uniform radius of curvature between the inner and outer circular edges. The anterior surface has two radii of curvatures providing for correction of myopia. The first radius of curvature extends from near the outer circular edge to a junction point before the inner circular edge. The second radius of curvature extends from the junction point and continues to the inner circular edge. The inner and outer circular edges have a thickness of less than about 0.020 mm, but preferably are about 0.010 mm or less.
U.S. Pat. No. 6,511,508 to Shahinpoor, et al., discusses surgical correction of human eye refractive errors such as presbyopia, hyperopia, myopia, and astigmatism by using transcutaneously inductively energized artificial muscle implants to either actively change the axial length and or the anterior curvatures of the eye globe. This brings the retina/macula region to coincide with the focal point. The implants use transcutaneously inductively energized scleral constrictor bands equipped with composite artificial muscle structures. The implants can induce enough accommodation of a few diopters, to correct presbyopia, hyperopia, and myopia on demand. In the preferred embodiment, the implant comprises an active sphinctering smart band to encircle the sclera, preferably implanted under the conjunctiva and under the extraocular muscles to uniformly constrict the eye globe, similar to a scleral buckle band for surgical correction of retinal detachment, to induce active temporary myopia (hyperopia) by increasing (decreasing) the active length of the globe. In another embodiment, multiple and specially designed constrictor bands can be used to enable surgeons to correct astigmatism.
U.S. Pat. No. 7,060,094 to Shahinpoor, et al., teaches surgical correction of presbyopia and hyperopia by a circularly distributed assembly of mini-bridges implanted between the interior surfaces of the ciliary muscle and the exterior surface of the lens capsule, for augmenting the transmission of the contraction force of the ciliary muscle/zonule assembly to the lens capsule. The lens is symmetrically squeezed by mini-bridges acting in concert with the ciliary muscle thus changing the curvature of the lens. The mini-bridges are composite synthetic muscles comprising either passive biocompatible mini-bridges made with polymer gels, silicone polymers or a composite, electromagnetically or mechanically deployable mini-bridges, inflatable balloons or synthetic muscles. The surgical procedure comprises using a ciliary muscle relaxant to stretch the lens/zonules/ciliary muscle assembly. An ultrasonic biomicroscope (UBM) is then used to enable the surgeon to see the area for implantation and the mini-bridges and thus perform endoscopic or incisional surgery to implant the mini-bridges in and around zonular cavities.
U.S. Pat. No. 7,090,696 to Shahinpoor, et al., teaches correction of eye refractive errors like presbyopia, hyperopia, myopia, and astigmatism using either pre-tensioned or transcutaneously energized artificial muscle implants to change the axial length and anterior curvatures of the eye globe by bringing the retina/macula region to coincide with the focal point. The implants are sclera constrictor bands, segments or ribs for inducing accommodation of a few diopters, to correct refractive errors on demand or automatically. The implant comprises an active sphinctering band encircling the sclera, implanted under the conjunctiva and under the extraocular muscles to uniformly constrict the eye globe, to induce active temporary myopia (hyperopia) by increasing (decreasing) the length and curvature of the globe. Multiple and specially designed constrictor bands enable surgeons to correct astigmatism. The artificial muscles comprise materials such as composite magnetic shape memory (MSM), heat shrink, shape-memory alloy-silicone rubber, electroactive ionic polymeric artificial muscles or etectrochemically contractile ionic polymers bands.